The development of novel functional compounds for use in electronic devices is currently the subject of intensive research. The aim here is the development and investigation of compounds which have hitherto not been employed in electronic devices, and the development of compounds which enable an improved property profile of the devices.
In accordance with the present invention, the term electronic device is taken to mean, inter alia, organic integrated circuits (OICs), organic field-effect transistors (OFETs), organic thin-film transistors (OTFTs), organic light-emitting transistors (OLETs), organic solar cells (OSCs), organic optical detectors, organic photoreceptors, organic field-quench devices (OFQDs), organic light-emitting electrochemical cells (OLECs), organic laser diodes (O-lasers) and organic electroluminescent devices (OLEDs).
The structure of organic electroluminescent devices (OLEDs) in which the compounds of the formula (I) can preferably be employed as functional materials is known to the person skilled in the art and is described, inter alia, in U.S. Pat. No. 4,539,507, U.S. Pat. No. 5,151,629, EP 0676461 and WO 1998/27136.
Further improvements are still necessary concerning the performance data of the organic electroluminescent devices, in particular in view of broad commercial use. Of particular importance in this connection are the lifetime, the efficiency and the operating voltage of the organic electroluminescent devices and the colour values achieved. In particular in the case of blue-emitting electroluminescent devices, there is potential for improvement with respect to the lifetime of the devices. In addition, it is desirable for the compounds, for use as functional materials in electronic devices, to have high thermal stability and a high glass-transition temperature and to be sublimable without decomposition.
In this connection, there is a need for alternative hole-transport materials for use in electronic devices. In the case of hole-transport materials in accordance with the prior art, the voltage generally increases with the layer thickness of the hole-transport layer. In practice, a greater layer thickness of the hole-transport layer would frequently be desirable, but this often has the consequence of a higher operating voltage and worse performance data. In this connection, there is a need for novel hole-transport materials which have high charge-carrier mobility, making it possible to achieve thicker hole-transport layers with only a slight increase in the operating voltage.
In accordance with the prior art, the hole-transport materials used in the hole-transport layer or in the hole-injection layer are, in particular, triarylamine derivatives which contain two triarylamino groups. These compounds are frequently derived from diarylamino-substituted triphenylamines (TPA-type), from diarylamino-substituted biphenyl derivatives (TAD-type) or combinations of these basic compounds. Furthermore, use is made, for example, of spirobifluorene derivatives which are substituted by two or four diarylamino groups (for example in accordance with EP 676461). In the case of these compounds, there continues to be a need for improvement, in particular with respect to efficiency, lifetime and operating voltage, both in the case of fluorescent and phosphorescent OLEDs, on use in an organic electroluminescent device and with respect to the thermal stability during sublimation.
Furthermore, so-called starburst amines are known from the prior art for use in OLEDs, Starburst amines, which contain three diarylamino groups which are bonded to a common central benzene ring, where the central benzene ring is unsubstituted at the remaining positions, are disclosed, inter glia, in EP 0611148 for the preferred use in a hole-transport layer. However, these compounds are only suitable to a slight extent for use as hole-transporting material in an emitting layer comprising blue- or green-phosphorescent emitter compounds.
There continues to be a need for alternative matrix materials for use in electronic devices. In particular, there is a need for matrix materials for phosphorescent emitters which simultaneously result in good efficiency, a long lifetime and a low operating voltage. Specifically the properties of the matrix materials are frequently limiting for the lifetime and the efficiency of the organic electroluminescent device. In particular, it is desirable for matrix materials for phosphorescent emitters for these to have a high T1 level (triplet level).
In accordance with the prior art, carbazole derivatives, for example bis(carbazolyl)biphenyl, are frequently used as matrix materials. Furthermore, ketones (WO 2004/093207), phosphine oxides, sulfones (WO 2005/003253), triazine compounds, such as triazinylspirobifluorene (cf. WO 2005/053055 and WO 2010/015306), and metal complexes, for example BAlq or zinc(II) bis[2-(2-benzothiazole)phenolate], are used as matrix materials for phosphorescent emitters. However, there continues to be a need for alternative compounds for use as matrix materials for phosphorescent emitters. In particular, there is a need for compounds with which an improvement in the performance data of the electronic devices can be achieved.